1. Field of the Invention
The present invention relates to a modified powder or particulate material coated on substantially the entire surface thereof with a film of a silicone polymer carrying at least one pendant group thereon. More specifically, it relates to a modified powder or particulate material obtained by coating a powder or particulate material with a film of a silicone polymer, and thereafter, carrying out an addition reaction to introduce a pendant group into the silicone polymer, whereby the surface activities of the powder or particulate material are disappeared, the unpreferable generation of hydrogen from the surface due to a coexisting H.sub.2 O or alcohol can be prevented, and various characteristics (e.g., dispersibility, UV absorbability) can be afforded to the powder or particulate material by appropriately selecting the pendant group.
The term "powder or particulate material" (i.e., "powder material" hereinbelow) used herein means any material generally having a particle size of 10 mm or less, but sometimes more than 10 mm. The agglomerates and the molded or shaped products of the powder material and the burned products thereof are also included in this term. According to the present invention, any powder material including an ultrafine powder having a size of 0.02 .mu.m or less can be modified.
The term "pendant group" used herein means a residue of a compound capable of reacting with an Si--H moiety, which residue is introduced to the silicone polymer by the addition reaction of the compound. This pendant group provides various characteristics or functions to the powder material.
The modified powder material according to the present invention does not denature or decompose perfumes, oils, or resins even when coexisting therewith, and therefore, will not cause problems such as denaturation, odor change, and color change and can be utilized in the fields of, for example, cosmetics, pharmaceuticals, resin compositions, coating materials, inks, paints, decoratives, fragrants, magnetic materials, and medical materials. Further, Si--H moieties contained in the silicone polymer film coating the powder material can be substantially eliminated or considerably reduced so that the powder material can be effectively formulated into, for example, an emulsion system. Furthermore, composite materials having various functions can be provided.
2. Description of the Related Art
Silicone oils have been frequently used in the prior art for the hydrophobic modification of a powder material. For example, Japanese Examined Patent Publication (Kokoku) No. 41-9890 discloses imparting lubricity to an animal, vegetable or mineral powder by coating the surface of the powder with a silicone resin coating material, followed by drying and baking. In Japanese Examined Patent Publication (Kokoku) No. 45-2915, a mineral powder such as talc is simply attached with a silicone having hydrogen directly bonded to silicone in the molecular chain by, for example, blender mixing, followed by heat baking, thereby imparting a water repellency to the powder. According to Japanese Examined Patent Publication (Kokoku) No. 45-18999, talc is attached with dimethylpolysiloxane or methylhydrogenpolysiloxane by contact with an organic solvent solution thereof, followed by baking optionally with the addition of a substance such as zinc octoate as the crosslinking polymerization catalyst for methylhydrogenpolysiloxane, thereby imparting a free flow property to the powder. Further, in Japanese Examined Patent Publication (Kokoku) No. 49-1769, titanium dioxide is subjected to direct coating, emulsion coating or solvent solution coating of various alkylpolysiloxanes, and then dried and baked optionally by using, in combination, an ester compound having a total carbon number of 6 or more, whereby the dust property, dispersibility, etc., of the powder are modified. On the other hand, in Japanese Unexamined Patent Publications (Kokai) Nos. 56-16404, 55-136213, and 56-29512, after mixing under stirring with the addition of silicone oils and oil agents or by the application of a mechanochemical reaction such as crushing, a baking treatment is performed.
Further, Japanese Unexamined Patent Publication (Kokai) No. 57-200306 discloses a method for imparting a water repellency and flow property to a powder without the application of a baking treatment by treating the powder with (A) a silane compound having a specific structure, (B) a cyclic polyorganosiloxane, and (C) a linear polyorganosiloxane. According to this method, 1 to 10% by weight based on the powder to be treated of the above organic silicone compound is adsorbed onto the powder by spraying a solution diluted in a solvent, direct spraying, or gaseous atomization, or by directly mixing under stirring, and then a water or water vapor treatment is applied. In the (B) cyclic polyorganosiloxane, the trimer having a methyl group is excluded, because it is solid and difficult to handle.
However, according to these methods, in most organic pigments and inorganic pigments, those weakly resistant to heat, such as yellow iron oxide or prussian blue, could not be treated.
For example, among the organic pigments, C.I. 15850:1 (lithol rubine BCA) could not be treated, because it was dehydrated at 80.degree. C. and changed crystal form from .alpha.-type to .beta.-type simultaneously with a change in tone. On the other hand, prussian blue is decomposed by the application of heat and gradually releases cyan gas at 150.degree. C. or higher. Baking treatment is carried out at 350.degree. C. for 2 hours, as a typical example of a higher temperature treatment, or at 150.degree. C. for 15 to 40 hours, as a typical example of a lower temperature treatment. Under such conditions, prussian blue not only undergoes a color change but also releases harmful cyan gas, thus being very dangerous.
Such a baking treatment of the prior art can be applied only for a part of stable inorganic pigments, and has the vital defect that treatment of an organic pigment which has a brilliant alters color its color tone.
We have found and disclosed, in our copending application entitled "Modified Powder or Particulate Material" Ser. No. 875,140, filed on June 16, 1986, that the above-mentioned disadvantages can be eliminated by a modified powder or particulate material produced by bringing a certain silicone compound in the form of a vapor into contact with the powder or particulate material. In the method disclosed in our said copending application, the silicone compound is brought into contact with the powder material and polymerizes thereon, and Si--H moieties are crosslinked on the surface of the powder material to form the silicone polymer film thereon. However, steric hindrance interferes with the proceeding of the crosslinking. Because the crosslinking does not fully proceed, i.e., unreacted Si--H moieties remain, the powder material obtained in our said copending application may be unstable under a severe alkaline or acidic condition.
A treatment with methyl hydrogen polysiloxane has an advantage that it can be carried out under a relatively low temperature. However, the powder material treated with methyl hydrogen polysiloxane does not always exhibit a sufficient stability, because it may cause generation of H.sub.2 under the coexistence of H.sub.2 O or an alcohol therewith, due to the remaining Si--H moieties present in the silicone polymer film formed on the powder material.
A hydrophobic nature can be imparted to the powder material by the treatment with, for example, methyl hydrogen polysiloxane. However, if a powder material having an optimum dispersibility in a given oil or resin is obtained, the powder material should be treated with an alkyl/aryl hydrogen polysiloxane having the specific alkyl or aryl groups selected with respect to the oil or resin. In some cases, it is necessary and possible to use the polysiloxane having long hydrocarbon residues. However, a boiling or melting point of such a polysiloxane is very high, and thus, it is difficult to treat the powder material with such a polysiloxane in the preferable forms thereof, i.e., vaporized polysiloxane.
Further, it is difficult to obtain the powder material coated with a film of the silicone polymer carrying various functional groups (e.g., --NH.sub.2, --COOH, --CN) thereon, because a treating agent containing Si--H moieties and such functional groups is not easily available.
A silane coupling agent is conventionally used so as to introduce the functional group to the powder material. For example, a silica can be easily treated with the silane coupling agent. However, there are some powder materials such as zinc oxide or titanium dioxide difficult to be treated with the silane coupling agent. Further, the silane coupling agent is introduced to, for example, the metal oxide, by the reaction with an OH group present on the surface of the metal oxide. Therefore, the functional groups introduced by the silane coupling agent cannot be firmly attached to the metal oxide. Furthermore, the treatment with the silane coupling agent does not result in the polymer film coating substantially the entire surface of the metal oxide. Thus, metal atoms are exposed on the surface thereof, and the surface activity of the metal oxide cannot be blocked. Therefore, the metal oxide treated with the silane coupling agent may cause problems such as denaturation and odor change when formulated in, for example, cosmetics. Further, although a hydrophobic nature can slightly be obtained, a dispersibility of the powder material cannot be controlled by such a treatment.